1. Field of the Invention
The present invention relates to a method of manufacturing a pneumatic tire, and more particularly to a method of manufacturing a pneumatic tire, which enables a pneumatic tire having excellent uniformity to be manufactured with high productivity by effectively using a rigid inner mold, the pneumatic tire having an inner layer which is light in weight and excels in air penetration preventing performance.
2. Background Information
Various methods of manufacturing a pneumatic tire, in which a green tire is molded on the outer peripheral surface of a metal rigid inner mold, and the molded green tire is placed inside a curing mold along with the rigid inner mold for curing, have been proposed as described, for example, in Japanese patent application Kokai publication No. 2001-88143 and Japanese patent application Kokai publication No. 2003-340824. The manufacturing method using such a rigid inner mold does not require a conventionally used bladder made of rubber, and can eliminates the process of, for example, detaching the molded green tire from a making drum. Moreover, compared with the case where a bladder is used for manufacturing, there is an advantage in that the inner peripheral surface of the cured tire can be formed into a predetermined shape with high precision.
However, because the green tire is pressed by the curing mold from only the outside during the curing, the pressing force acting on the inner peripheral surface of the green tire is small. Accordingly, for example, even when non-uniformity in the volume of the tire constituting members exists on the inner peripheral surface of the tire, it is difficult to correct the non-uniformity, and thus improvement in uniformity of the cured tire is limited.
In addition, when the inner peripheral surface of the green tire is pressed by the outer peripheral surface of the rigid inner mold, spaces between divided bodies forming the rigid inner mold leave marks on the inner peripheral surface of the cured tire, and thus there is a problem of reduced appearance quality.
Furthermore, although butyl rubber is mainly used for an inner layer (innermost peripheral surface) of the green tire, an additional work of, for example, applying release agent is needed in order to easily release the inner layer from the outer peripheral surface of the rigid inner mold. Using an inner layer formed of butyl rubber is disadvantageous in reducing the tire weight because an inner layer formed of butyl rubber needs a certain thickness to secure sufficient air penetration preventing performance. For this reason, an inner layer which is light in weight and excels in air penetration preventing performance has been demanded.
Furthermore, in the conventional manufacturing method using a rigid inner mold, the rigid inner mold is placed inside the curing mold along with the green tire during the curing, and thus there is a problem in that the rigid inner mold cannot be used for molding the green tire during the curing.
Consequently, for example, in order to increase the production volume of tires, an accordingly large number of rigid inner molds are needed.